A stereo headset amplifier driving unit in audio applications is configured to drive an audio signal across a speaker coupled to the amplifier. The stereo headset amplifier driving unit includes a chip located in an audio system (e.g., mobile phone), and the speakers include a pair of earphones coupled to the audio system. A constituent driver amplifier of the driving unit is powered by a supply voltage, a fraction of which may bias the audio output of the driver amplifier. When the speaker is coupled to the headset amplifier driving unit, the DC bias across the speaker contributes to undesired power dissipation. Additionally, noise in the circuit will be audible across the speaker over the DC bias as a hum.
Schemes utilized in removing the DC bias in the audio output across the speaker may include a capacitive scheme configured to decouple the DC bias from the audio output, a common mode (CM) amplifier scheme having an extra CM amplifier to generate a CM voltage equal to the DC bias in the audio output, and a “negative voltage” scheme configured to enable the audio output to swing below a ground voltage. The “negative voltage” scheme involves generation of a negative supply voltage from the positive supply voltage through a charge pump. In the capacitive scheme and the CM amplifier scheme, the noise across the speaker coupled to the headset driving unit is dependent on a reference voltage input to the driver amplifier and/or the CM amplifier configuration. The “negative voltage” scheme solves the aforementioned problems associated with the capacitive scheme and the CM amplifier scheme, but causes increased power consumption from the positive supply voltage. Moreover, the generation of the negative supply voltage through the charge pump necessitates the use of an extra processing mask for creation of a deep N-well. Thus, there is an increased area/cost requirements associated with the “negative voltage” scheme.